Neutron scattering is a very powerful technique complementary to X-ray scattering for the study of the matter organisation. The neutron scattering techniques provide a powerful means of characterising the structural organisation at the scale of a few Angstroms (Å) up to a few hundred and even a few thousand Angstroms. Unlike X-ray scattering in which the X-radiation interacts with the electronic cloud of atoms, neutrons interact with the atomic nuclei of the sample. The resulting scattering is specific to each isotope, very different particularly for the hydrogen and the deuterium, so that an isotopic contrast can be created in organic materials. Furthermore, unlike X-rays techniques, the neutron scattering technique is a non-destructive method and presents a much higher penetration length than the X-radiation.
The neutron scattering technique associated with two-dimensional position sensitive image integrating detectors enables two-dimensional observation of the scattering space.
A first group of detectors is composed of gas detectors combined with wire chambers (see R. Allemand, J. Bourdel, E. Roudaut, P. Convert, K. Ideb, J. Jacobe, J. P. Cotton, B. Farnoux, “Nucl. Instr. Meth.”, 126, 29 [1975]; Y. Giomataris, Ph. Rebourgeard, J. P. Robert, G. Charpak, “NIM” A376 [1996] 29; C. Petrillo et al., “Nucl. Instr. and Meth” A378 [1996] 541 & A424 [1999] 523; G. Brickner et al, “Nucl. Instr. and Meth” A392 [1997] 68). This detection category is usually devoted to the study of neutron scattering phenomena at small angles. These spectrometers have a low spectral resolution.
A second group of two-dimensional detection instruments is composed of devices of the Image Plate type (C. Wilkinson et al, “Neutrons, X-Rays and Gamma Rays” 1737[1992] 329) that comprise a scintillator coupled with a laser. This principle comprises 3 steps; the first consists in charging the scintillating plate, the second in reading the plate using a laser for revealing the number of charges, and finally the incrementation managed by computer. This technique is widely used for X-rays diffusion and is still very difficult to be adapted for the neutrons use.
Observation at wide angles is usually carried out by scanning the reciprocal space along a single direction rather than two directions simultaneously; this is the case for linear multi-counters or 2 or 3-axis elastic diffusion spectrometers.
Nevertheless, two-dimensional observation at wide angles is important for the study of the local organisation, and particularly in the case of structured materials and/or fluids subjected to the action of anisotropic stresses such as pressure gradients, fluid flow, etc.
Neutronography usually consists in using an incident polychromatic neutron beam placed on the trajectory of a sample, to reveal a picture of the transmission/absorbing properties through the sample.
A detector in the neutronography domain has been proposed (see S. Koemer, E. Lehmann, P. Vontobel, “Nucl. Inst. and Meth.” A454 [2000] 158-164) that uses a scintillator sensitive to neutrons coupled to a charge-coupled detector. Nevertheless, this detector is not adapted to a quantitative measurement of the signal, and is not enough sensitive for a quantitative characterisation of the organisation of a material at molecular or atomic scale.
It is therefore a goal of the invention to provide a two-dimensional detection system for neutron radiation that enables a quantitative detection of the number of neutrons scattered by a sample, particularly at wide diffusion angles, and that further overcomes at least one of the above-mentioned disadvantages.